Electrolytic method for fabricating transparent conductive multi-component metal oxide powders

ABSTRACT

An improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders is disclosed. By adjusting pH-value, the metal compositions that a transparent conductive oxide film requires are electrolyzed to form individual metal ion precursory solutions under the condition not to precipitate the solution. Then, the individual metal ion precursory solutions with the required composition ratio are mixed and the precipitate reaction is performed. Finally, transparent conductive multi-component oxide powders with the controlled composition ratio and composition homogeneity are obtained by calcining the washed, filtered, and dried co-precipitates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating transparent conductive multi-component metal oxide powders, particularly to an improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders that a transparent conductive oxide film requires.

2. Description of the Related Art

Transparent conductive oxide (TCO) films are films having good electrical conductivity and high visible light transmittance. TCO films are important materials for transparent conductive electrodes used in photoelectronic devices due to their characteristics of high conductivity (the resistivity is less than 2×10⁻⁴ Ωcm and is about 100 times the resistivity of silver), high visible light transmittance, and high infrared light reflectance. TCO films are made of the semiconductors with energy band gap larger than the energy of the visible light. Impurity doping in the TCO semiconductors enhances their conductivity. For example, ITO is formed by doping tin in indium oxide; and AZO is formed by doping aluminum in zinc oxide. Since the TCO films have been massively used in display panels, touch panels, solar panels, and other photoelectronic products, the developments of the sputtering targets used to deposit TCO films and the transparent conductive multi-component metal oxide powders used to prepare TCO sputtering targets have become important issues in related fields.

Presently, the process for fabricating transparent conductive multi-component metal oxide powders includes solid-state reaction, coprecipitation method, sol-gel method, and electrolytic method. The electrolytic method is a chemical reaction process in which metals are dissolved to form metal ion solutions by electrolytic action of electrical current and the metal ion solutions are precipitated under controlled condition such that transparent conductive multi-component metal oxide powders are fabricated. Currently, there are three types of electrolytic methods:

(1) Mixing the individual single component metal oxide powders obtained by electrolyzing individual metals respectively to produce the doped transparent conductive multi-component metal oxide powders (for instance, electrolyzing indium and tin respectively)

In this method, the electrolytic and the precipitation processes are carried out under neutral pH condition. Then, individual single component metal oxide powders are prepared through processes of washing, filtering, drying, and calcining. The advantages of this method include reduced particle size and enhanced powder purity. Besides, a large amount of pollutants from strong acids and precipitants can be avoided. However, if transparent conductive multi-component metal oxide powders are fabricated by this method, different metals have to be electrolyzed separately, and, then, the two single component metal oxide powders have to be mixed and reacted by the solid-state reaction process to obtain the transparent conductive multi-component metal oxide powders. Since the homogeneity and composition for mixing the metal oxide powders are limited and the impurity emerges during milling process, the properties of the sputtering target and transparent conductive oxide film are both influenced.

(2) Simultaneously electrolyzing metals to produce the doped transparent conductive multi-component metal oxide powders.

In this method the electrolytic and the precipitation process are carried out for all the component metals under neutral pH condition. Then, the doped transparent conductive multi-component metal oxide powders are prepared through processes of washing, filtering, drying, and calcining. In addition to the advantages of the method (1), mixing of all the component metal oxide precursor powders in the solution can reduce the disadvantages for the solid state reaction in the following steps. However, this method requires more electrolytic equipments to perform the electrolytic process. Also, the required composition of the transparent conductive multi-component metal oxide powders can only be obtained by precisely controlling the electrolytic condition. Furthermore, respective metal oxide precursor powders require different pH condition to be fully precipitated, which results in the incomplete precipitation and the incorrect composition of the transparent conductive multi-component metal oxide powders. Finally, the precipitation reaction occurs near individual metal electrode and additional mixing process is required to produce TCO precursor precipitates. Therefore, the composition of transparent conductive multi-component metal oxide powders fabricated by this precursor precipitates may be inhomogeneous.

(3) Electrolyzing the alloys with the desired metal composition to produce transparent conductive multi-component metal oxide powders.

In this method the electrolytic and the precipitation process are carried out for the alloy with the desired metal composition under neutral pH condition. Then, the doped transparent conductive multi-component metal oxide powders are prepared through processes of washing, filtering, drying, and calcining. This method has the advantages identical to the method (2). Although the method is easier than the method (2) in the fabrication process and equipment, the metal alloys with different composition have to be used to fabricate the transparent conductive multi-component metal oxide powders with different composition. Not only the alloy raw material cost is greatly increased but also the parameters of the electrolytic process need to be adjusted as well. Furthermore, respective metal oxide precursor powders require different pH condition to be fully precipitated, which results in the incomplete precipitation and the incorrect composition of the transparent conductive multi-component metal oxide powders.

In conclusion, during the process for obtaining transparent conductive multi-component metal oxide powders, the existing electrolytic method can reduce the particle, enhance the purity the powders, and decrease the a large amount of pollutions. However, the problem for controlling the composition of the powders is not still solved such that the properties of the sputtering target and the transparent conductive multi-component metal oxide powders in the succeed process are not good.

SUMMARY OF THE INVENTION

In view of the problems and shortcomings of the prior art, a primary objective of the present invention is to provide an improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders, which has the advantages for the existing electrolytic method, modifies the technology for controlling the composition of the powders, and enhances the properties of the powders, whereby the properties of the sputtering targets and the TCO films fabricated in the succeeding sputtering process are enhanced.

To achieve the abovementioned objectives, the present invention discloses an improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders. Firstly, the pH of an electrolytic solution is adjusted so as not to produce precipitates. Next, metals that transparent conductive multi-component oxide powders require are dissolved into individual metal ion precursor solutions by the electrolytic method. Then, the individual metal ion precursor solutions with the required composition ratio are mixed to form a clear multi-component oxide precursor solution. A precipitant is then added into the multi-component oxide precursor solution to adjust its pH. When the designated pH is reached, the precursor co-precipitates are fully precipitated. Finally, transparent conductive multi-component metal oxide powders with required composition are obtained by washing, filtering, drying, and calcining the obtained precursor co-precipitates.

The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders of the present invention not only has the advantages for the existing electrolytic method but also avoid the incomplete precipitation in the existing electrolytic process, whereby the problems of the powders with incorrect and non-homogeneous composition are solved. Besides, the transparent conductive multi-component metal oxide powders fabricated by the present invention not only have reduced particle size and enhanced purity but also reduce pollutants created during the electrolytic production process, whereby the properties of the TCO multi-component metal oxide powders greatly are enhanced. Also, TCO sputtering targets and TCO film fabricated by these TCO powders possess good properties.

Below, the embodiments are described in details with the aids of the attached drawings to enable clear understanding of the objectives, technical contents, characteristics and accomplishments of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart showing an improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders;

FIG. 2 is a XRD showing the fabricated transparent conductive multi-component metal oxide powders according to an embodiment of the present invention; and

FIG. 3 is a SEM showing the fabricated transparent conductive multi-component metal oxide powders according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses an improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders that TCO films require. According to the electrochemistry theorem, two electrodes are applied with a DC electric field and a metal that is to be electrolyzed is used as the anode. After the electrolytic process starts by applying the DC current, the pH value of the electrolytic solution is adjusted to a specific value by adding acid or alkali. Positive and negative ions in the electrolytic solution conduct the electrical current so that the oxidation and the reduction reactions occur at the electrodes. Since the oxidation reaction occurs at the anode, the metal loses electrons to become ions in the electrolytic solution. Since the reduction reaction occurs at the cathode, different ions are combined with the electrons to become reduced. Then, a clear metal ion solution is obtained. Mixing the required individual clear metal ion solutions forms a multi-component oxide precursor solution with the required composition and the composition homogeneity. Next, the multi-component metal oxide precursor co-precipitate is obtained by adding a precipitant to control the pH for precipitating. Finally, the washing, filtering, drying, and calcining processes are sequentially performed to produce transparent conductive multi-component metal oxide powders.

Next, refer to FIG. 1, which is a flowchart showing the improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to an embodiment of the present invention.

Firstly, in Step S100, an electrolytic equipment is set up. A prepared electrolytic metal (indium) is used as the anode, and an adaptive material (such as stainless steel or graphite board) used as a cathode is selected. Also, an electrolytic solution is placed in an electrolytic reactor. The composition of the electrolytic solution comprises NH₄Cl or NH₄NO₃. The concentration of the electrolytic solution is between 0.5M and 3M.

In Step S110, the pH-value of the electrolytic solution in the electrolytic reactor is adjusted by adding acid or alkali. The pH of the electrolytic solution is preferably adjusted to between 0.5 and 3.5.

Next, in Step S120, after the required pH is reached, the electrolytic conditions (such as voltage, current, temperature, and electrolytic time, wherein the temperature ranges between 10° C. and 50° C.) are adjusted. Then, the metal is electrolyzed to form a clear first precursor metal ion solution required.

Afterwards, in Step S130, a clear second precursor metal ion solution and the clear first precursory metal ion solution are mixed with the required composition, so as to form a multi-component oxide precursor solution with the required component and composition homogeneity. Wherein, the clear second precursor metal ion solution is fabricated by electrolyzing metal or dissolving metal salts directly in Step S120.

In Step S140, precipitates are completely precipitated by adding a precipitant to control the pH for precipitating the multi-component oxide precursor solution. The precipitant is NH₄OH, NaOH, or KOH; and the pH of the multi-component oxide precursor solution is adjusted to between 5.5 and 9.5. In this step, a co-precipitate solution is produced. And the co-precipitate solution is filtered to obtain a filter cake.

Finally, in Step S150, the filter cake is placed in dioxide water for filtering, and the washing process is repeated to obtain co-precipitate compound powders. Transparent conductive multi-component metal oxide powders are fabricated by calcining the dried precipitate compound powders. The transparent conductive multi-component metal oxide powders of the present invention comprise tin doped indium oxide (ITO) or zinc doped indium oxide (IZO), aluminum doped zinc oxide (AZO), or gallium doped zinc oxide (GZO).

Below is the description of the specific embodiment of the present invention.

Indium and a graphite stick are respectively used as the anode and the cathode in the embodiment. NH₄NO₃ used as the electrolytic solution is placed into the electrolytic reactor. Next, when the pH of the electrolytic solution is equal to 1 by using nitric acid, the current of 4 A is applied to perform the electrolytic process for 30 minutes. Afterwards, the weight variation of indium is measured, and SnCl₄ is added such that the weight percentage of In₂O₃/SnO₂ is equal to 90/10. Then, the clear ITO precursor solution is obtained by mixing them well. After ammonia is poured into the obtained solution to adjust the pH-value thereof to 7.0, the washing, filtering, and drying processes are performed. Then, the calcining process is performed at 800° C. for 3 hours, so as to obtain the ITO powders.

In addition, the material properties of the powders are further analyzed by X-ray difftaction (XRD) and Scanning Electron Microscope (SEM). As shown in FIG. 2 and FIG. 3, which are respectively the results for XRD and SEM. The experiments prove that the fabricated powders are crystalline ITO powders by FIG. 2 and that the crystalline ITO powders are nano-scaled powders. In other words, the fabrication method of the present invention can produce the nano-scaled ITO powders.

Furthermore, in the embodiment, the fabricated ITO powders are pressed and sintered to produce ITO target, which is compared with the existing commercial target, as shown in Table 1. Table 1 shows the comparison of the electrical properties and density measured by the Archimedean method and the Four-Point probe method, which proves that the fabrication method of the present invention can produce the ITO target having the properties like the commercial target.

TABLE 1 Four-Point Archimedean method probe method Volume Weight Green Density Resistance Coefficient Sample (cm³) (g) (g/cm³) (Ω · cm) Commercial 3.212 22.73 7.08 2.55 * 10−4 Target-1 Commercial 3.205 22.743 7.1 2.55 * 10 * 4 Target-2 Electrolytic 3.108 22.066 7.1 2.40 * 10−4 Target of the embodiment

According to the improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders of the present invention, the precursor solutions of the individual metal ions are firstly formed. Then, the individual metal ion precursor solutions are mixed with the required composition ratio and the precipitate process is performed in order. Thus, the transparent conductive multi-component metal oxide powders with the controlled composition ratio and high composition homogeneity are obtained. Therefore, the present invention not only has the advantages of the existing electrolytic method for reducing particles, enhancing powders homogeneity, and decreasing environment pollutions without using a large amount of strong acid but also enhances the accuracy and homogeneity of the powders composition. As a result, the properties of the fabricated transparent conductive multi-component metal oxide powders are greatly improved and the properties of the target and film of transparent conductive oxide fabricated by the powders are effectively enhanced in the succeed process.

The preferred embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the characteristics or spirit of the present invention is to be also included within the scope of the present invention. 

What is claimed is:
 1. An improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders comprising steps of: placing a prepared electrolytic metal used as an anode in an electrolytic solution; adjusting a pH of said electrolytic solution; performing an electrolytic process to form a clear first precursor metal ion solution; adding and mixing a clear second precursor metal ion solution to obtain a multi-component oxide precursor solution; and adding a precipitant to vary a pH of said multi-component oxide precursor solution and precipitate said multi-component oxide precursor solution, whereby transparent conductive multi-component metal oxide powders are obtained.
 2. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein said precipitant is added to produce a co-precipitate solution, and said step of adding said precipitant further comprises steps of: filtering said co-precipitate solution to obtain a filter cake; washing and filtering said filter cake to obtain co-precipitate compound powders; drying said co-precipitate compound powders; and calcining said co-precipitate compound powders to obtain said transparent conductive multi-component metal oxide powders.
 3. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein composition of said electrolytic solution comprises NH₄Cl or NH₄NO₃.
 4. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein concentration of said electrolytic solution is between 0.5M and 3M.
 5. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein in said step of adjusting said pH of said electrolytic solution, said pH of said electrolytic solution is adjusted to between 0.5 and 3.5.
 6. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein in said step of performing said electrolytic process, a temperature ranges between 10° C. and 50° C.
 7. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein said second precursory metal ion solution is fabricated by electrolyzing metal or dissolving metal salts directly.
 8. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein said precipitant is NH₄OH, NaOH, or KOH.
 9. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein in said step of adding said precipitant to adjust said pH of said multi-component oxide precursory solution, said pH of said multi-component oxide precursory solution is adjusted to between 5.5 and 9.5.
 10. The improved electrolytic method for fabricating transparent conductive multi-component metal oxide powders according to claim 1, wherein composition of said transparent conductive multi-component metal oxide powders is tin doped indium oxide (ITO) or zinc doped indium oxide (IZO), aluminum doped zinc oxide, or gallium doped zinc oxide. 